I noticed the rerating from this past week caused the change of my kid’s live rating which also impacted the Jan supplement. After I looked into it, the discrepancy came from this event. US Chess . That is a foreign fide event and I used the calculator to validate and found out his event should increase her rating by 10 points, but the last rerate made it a -6 points. Even the legacy system had a +5 points on this event. US Chess MSA - Cross Table for XIV Pan-American School Chess Championship STD U09 Girls (Event 202509052292)
I am not sure how it is calculated in the new system, but I really don’t think 6.5/7 should lose rating in this event.
thanks for the reply. Yes, the calculation is based on the players with published FIDE ratings. The link I attached is all about USCF conversions with ONLY players with published FIDE rating, otherwise the result would be 8.5/9. The recently rerated adjustment does not make sense, and it has a big discrepancy compared to the old adjustment previously posted on MSA.
Us chess rating regulations (white pages) has two provisions for converting fide ratings for us chess rating. The regular conversion formula, and the scholastic conversion formula. It is theoretically possible that the new system used the main conversion formula, and MSA used the scholastic formula. This could theoretically account for the discrepancy. If this is the issue I am somewhat suprised it would make such a difference though. As generally the difference in conversion formulas is usually only 1-3 rating.
I could get out a pen and paper and do the math to confirm if it is a different conversion formula (it would take about 5-10 minutes)
Mike Nolan, and ratingsmgr@uschess.org would have a better answer for you than myself. I am happy to do the math and see if there is anything to this theory if you request.
Did you start by converting the FIDE Ratings to US Chess ratings using the current conversion formula (in the rating supplement white paper)?
That’s the first step that the ratings program will do.
I am on the road and won’t be able to do much about this until January. If you can send me full details, I can pass them on to the person who wrote the new ratings programming to have him check that FIDE adjustment. I would not expect an answer from him until next week.
When I signed up the opt in foreign FIDE event, I was expecting people use the conversion formula on USChess website. But surprisingly, USCF rating office just simply used the exact FIDE rating for USCF rating adjustment, without any math conversion for the 2 foreign FIDE events my kid attended.. I thought that is how it is done in reality and my calculation was also just simply using the FIDE rating for USCF rating, and it is still way off.
Both of the rating adjustments (MSA and MUIR) were using the exactly same FIDE rating for USCF rating for calcuation without any conversion formula. (meaning USCF rating = FIDE ratring, instead of USChess = 932 + 0.564*FIDE if FIDE <= 2000)
I thought it is how things done in reality and used the already “underrated” opponent’s converted USCF rating (FIDE rating) to calculate, still it shows it should be +10 points instead of -6 points.
Events for younger players like the World Youth Championships use a different FIDE-TO-USCHESS conversion formula. We do not show the converted rating on the crosstable, only their published rating for that event.
I went ahead and got out a Pen, and Paper and I did the Math.
It turns out the new system is using the main FIDE Conversion formula instead of the Scholastic conversion formula for youth international events.
Concerning event# 202509052292 ID#30721310 gains 5 US Chess rating points when using the Scholastic formula in Chapter 6, and loses 6 US Chess rating points when using the main FIDE conversion formula in Chapter 2 (I used the formulas from the white pages, dated July 26, 2025).
I think you might need to open a ticket for this issue, unless there is already a ticket open addressing this issue (all International FIDE events are likely using the main conversion formula in Muir regardless if they are youth or open events)
I suppose theoretically the rating’s committee could have a meeting, and could decide to use a single conversion formula instead of having two for the sake of simplicity (Personally I like the Scholastic conversion formula in chapter 6, and I hope it stays. I know my opinion on the matter is about as valuable as a half penny though!)
I’m not sure where the alternate formula usage is coded in the MUIR data structure, I know we static tested it with youth formula flagged events, it may just be a function of getting it coded right.